EMC or the Electromagnetic Compatibility is defined as the ability of electronic equipment and systems to keep the ratios of useful signals to interference signals such that the performance characteristics of the equipment are not impaired when they are simultaneously used for their intended purpose in an acceptable environment.
The more exacting EMC requirements impose ever more requirements on electric and telecommunications equipment. The equipment must withstand interference of certain type and level. Also the equipment must not radiate too much interference into the environment.
Enclosures must be used in radiotelephones due to the EMC protection in order to decrease radiation emission and to increase the radiation tolerance of sensitive parts. The enclosures will contain several components, requiring a cover which can be opened for service and repair works in order to reach the components inside the casing.
In order to obtain an enclosure which can be opened there is used a separate cover, as is well known, which along its edges can be fastened to the frame of the EMC enclosure, thus coming into an electric and galvanic contact. This known construction has a disadvantage in that manufacturing a separate cover and fastening it to its frame causes material and labour costs. A separate cover also introduces a component item or the radiotelephone, the handling and updating of which causes extra costs.
In the known construction there can be a poor contact between the cover and the frame due to tolerances, or the cover contact could be insufficient, due to oxidation or high frequency characteristics. Then at high frequencies the cover or a part of it will rise to an impedance and begin to radiate or to receive radiation. The protective effect of the EMC enclosure or a part of it is then lost.
In practice there are several enclosed parts within the radio unit, whereby the above mentioned disadvantages have a large effect. On the other hand only a few EMC enclosures must be opened for service or repair. Therefore most covers are unnecessary components, as they must not be opened during the lifetime of the radiotelephone. Individual covers, due to oxidation reasons and the increase of the number of components, partly impair the reliability and further the impairment of performance characteristics due to any internal interferences.
An objective of the present invention is to provide an EMC enclosure, which should be of high quality and save costs compared with prior solutions.